When being mixed in a resin matrix, glass flakes improve the strength and dimensional accuracy of resin molded products. Glass flakes are used as pigments, are mixed in cosmetics, or are mixed, as a lining material, in paints that are to be applied onto surfaces of substrates such as, for instance, metals and concretes.
Glass flakes exhibit a metallic color when their surfaces are coated with a metal. Glass flakes also exhibit an interference color that is obtained through the interference of reflected light, when their surfaces are coated with a metal oxide. The glass flakes having a coating film formed of a metal or a metal oxide are preferred for use in applications such as paints and cosmetics where color tones and glossiness are regarded as important.
JP63(1988)-201041A discloses C-glass, E-glass, and sheet-glass compositions as those suitable for glass flakes. JP9(1997)-110453A discloses alkali-resistant glass flakes. JP2001-213639A discloses glass flakes having excellent chemical resistance and strength. JP63(1988)-307142A and JP3(1991)-40938A describe glass flakes with high ultraviolet absorptivity.
Glass flakes that have a surface coated with a metal or a metal oxide and that have improved colorability, light reflectivity, and shielding ability have been commercially available. For example, JP2001-31421A discloses a method of depositing rutile titanium dioxides and glass flakes with the rutile titanium dioxides deposited thereon.
Glass containing a large amount of transition metal oxides therein, which is not a glass flake though, has been known as glass with low visible-light transmittance. For instance, JP9(1997)-71436A describes absorber glass or fiber optic plate glass that has a wide absorption band extending from the ultraviolet region to the near infrared region. This absorber glass or fiber optic plate glass has a composition including La2O3 and BaO. JP2003-526187A describes a glass spacer. This glass spacer contains BaO or/and La2O3.
In the conventional glass flakes described above, no consideration was given to the visible-light absorptivity of the glass flakes themselves. The glass flakes contain a small amount of components that absorb visible light. Glass flakes disclosed in JP63(1988)-307142A and JP3(1991)-40938A exhibit excellent absorption properties with respect to the regions extending from the ultraviolet region to near ultraviolet region. However, they also contain a small amount of components that absorb visible light.
Accordingly, when a coating film is formed of a translucent material on the surfaces of conventional glass flakes, a color affected by the color of the substrates may develop. This is because the glass flakes hardly absorb visible light.
This phenomenon is described with reference to FIG. 7. A glass flake 31 has a translucent metal oxide film 32 on its surface. The glass flake 31 has been mixed as a pigment in a paint 6. The glass flake 31 itself has little visible-light absorptivity and the metal oxide film 32 is translucent. Accordingly, part of the light 21 that is incident on the glass flake is reflected, which becomes reflected light 22, but most part thereof is transmitted through the glass flake, which becomes transmitted light 23. The transmitted light 23 is reflected by the surface of a substrate 5, which becomes reflected light affected by the color of the surface.